Ignition system



Aug. 22, 1950 J. v. McNuLTY IGNI'rIoN SYSTEM Filed Dec. 11, 1944 INVENTOR.

ATTORA/EY Patented Aug. 22, 1950 IGNIrioN SYSTEM John V. McNulty, Binghamton, N. Y., assignor to Bendix Aviation Corporation, New York, N. Y., a corporation of Delaware Application December 11, 1944, Serial No. 567,672

3 Claims.

This invention relates to electrical apparatus z and more particularly to electrical circuits and parts thereof adapted for use in the ignition systems of internal combustion engines or the like.

One of the objects of the present invention is to provide a novel ignition system wherein electrical current is distributed at relatively low voltage and high frequency to a plurality of transformer coils mounted in or adjacent to the spark plugs of an engine or other spark gap at which a spark discharge is desired.

Another object of the invention is to provide an ignition system wherein novel means are employed for timing the successive electrical discharge or impulses for creating sparks atthe spark plugs in predetermined succession and at intervals determined by the speed of the engine on which the system is installed.

Still another object is to provide a condenser discharge type of ignition circuit to which energy is supplied by a magneto generator and wherein a high sparking rate is attainable across a spark gap in circuit with a storage condenser adapted to be charged by the magneto generator.

A further object is to provide a low voltage distribution ignition system, the novel construction of which makes it possible to employ a very small and light high frequency transformer coil at or near the spark plug for delivering the desired high voltage across the gap of the spark plug.

A still further object is to provide a condenser discharge type of circuit wherein the storage condenser is caused to discharge periodically across a novelly constructed spark gap device.

Another object is to provide a novel ignition circuit of the above character wherein the life and dependability of the control gap for the storage condenser are greatly enhanced.

Still another object is to provide a system of the above Character which is so constructed that a lower distribution voltage than has been heretofore used in simliar systems may be safely and effectively used, thereby reducing the radio shielding problems and minimizing electrical losses and failures.

A still further object is to provide a novel condenser discharge type of circuit wherein the electrodes of the control spark gap across which the condenser discharges may be spaced further apart than in prior systems using the same discharge voltage.

Another object is to provide a novel spark gap device adapted for use in a condenser discharge type of electrical circuit.

The above and further objects and novel features of the invention will more fully appear from the following detail description When the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and not intended to define the limits of the invention, reference for this latter purpose being had primarily to the appended claims.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

Fig. 1 is a diagrammatic view of an ignition system for an internal combustion engine which illustrates one form of the present invention;

Fig. 2 is a similar view showing another embodiment or modification of the invention; and,

Figs. 3 and 4 are top yand side elevation views, respectively, of a novel spark gap device adapted for use in the circuits of Figs. 1 and 2.

In the two. embodiments or modifications of the invention illustrated in the drawings, byway of example only, the invention is shown in its application to ignition systems for internal combustion engines wherein electrical energy is generated and supplied by a magneto type generator and distributed at relatively low voltage and relatively high frequency. Such systems are operable at all altitudes attainable by modern aircraft with a minimum danger of electrical failures and a minimum of electrical losses. The radio shielding difiiculties vand requirements are also substantially reduced in such systems. As shown, the main source of energy in both of the illustrated. embodiments comprises a magneto generator IO which may be in the form of any of many known types of magnetos. The particular type of magneto illustrated comprises a fourpole magnetic rotor Il and a two-pole stator |2, the poles of which are connected by a core on which is wound a coil vhaving a primary winding 13 and a secondary winding M. The relationship of these windings may be varied for obtaining any desired voltage in the secondary circuit.

In accordance with common practice, primary winding |3 has the opposte ends thereof connected to the points of a circuit breaker IB. Suitable resilient means, such as a spring 16, may be provided for normally urging said points toward closed or engaged position and suitable means, such as a rotatable cam H, may be provided for periodically moving said points to open or disengaged position to'interrupt the primary circuit. One side of the primary circuit is connected to ground, as at |8, and a condenser IS is connected across the points of circuit breaker to reduce sparking when the points are moved to open position.

For a purpose to appear hereafter, secondary winding |4 is tapped at approximately the center thereof and connected to ground as at |3, thereby making, Vin eifect,-.two secondary Windings. The ends or high potential v'turns of the secondary winding |4 are connected to the input terminals of a full wave point-to-plane type of rectifier 207 which may be of the cold cathode type known commercially as a Raytheon No. CK1004 gaseous tube rectifier. Thus, as rotor `'is-rotated. alternating current is induced in the primary circuit described above in a manner well understood in the art. When the primarycircuit is interrupted by the opening of the points or contacts' of circuit breaker |5 at predetermined intervals, usually when the primary'current is at about its maximum value; current'at-a' higher'voltage is induced in the secondarywinding |4, successive impulses being of *opposite' polarity, With the parts connected in the "mannerdescribed above, the'impulses of one polarity in' the secondary circuit will flow' throu'ghfrectifierO by way of one input terminal thereof and impuls'es of the-'opposite-polarity, will flow 'through the rectifier by Way of its other input terminal so that'the output of the rectifier is unipolar.

In'both' of vthe ill'usti'atedembodiments, the plate'or output' terminal 'of' rectifier`` 20' is connected to one terminal of a storage condenser 2 I, the other terminal of which is' connected to ground, as at 22. It is a characteristicv of rectifiersof the type mentioned that'current will flow therethrough only, from" point-to-plane, and not in'theopposite direction. Accordingly, the impulses passing 'through' the' rectifier' are efiective to `charge condenser 2| but'the'latter cannot discharge back through* the 'rectifier andv the coil of the magneto; In order to render the rectifier conductive; the'maximum'voltager delivered in the 'secondary circuit of the'magnetoat the minimum Operating; speed th'ereofimust'be'at least as great'as the on-set voltage: of therectifier and is 'preferably a hundred 'or`more volts. higher in order to provide a margin'br'factor ofsafety. For example, if theonlset 'voltageiof the rectifier is '900 volts, Vthe secondary voltage of the magneto at minimum Operatingv speed is preferably about' 1,000 volts'or'more: The voltage. ofthe charge stored on condenser 2| may beivaried by varying thei capacity of `the condenser. Knowing the energy supplied'tol the condenser by the magneto secondary,,it is possible to choose a condenser with'the desired capacity to obtain a desired voltage across the` condenser.

Referring morev particularly'now to the embodiment of Fig. 1,' thehighpotential'side 'of condenser 2| is connected to one of the main'electrodes 23' of'a novel spark gap' devicev 24 which Willbe more fully described hereafter. The other main electrode 25 of said device is connected'to theV inputterminal'oflan ignition distributor 28 which may be of any suitableknown' design but is preferably of :tlie'sliding carb'on brush type having a rotating element' 21 for distributing current'at relativelyv low voltage; Each of the output terminals 28" of the" distributor is connected* to a* primary winding' 29' of a high frequency transformer coil, the' secondary'winding 30=of which 'is connected across the'terminals of a spark plug or spark gap 3|; In accordance with conventional practice, one'terminal 'of'the spark plug and the low potential turns of the windings 29 and 30 are connected to ground as at 32. Thus, when the charge on condenser 2| reaches a sufficiently high voltage and is permitted to discharge across gap 23, 25, this high frequency discharge passes through a primary winding 29 selected by distributor 2G and induces a sufficiently high voltage in the secondary winding coupled therewith to create a spark or Shower of Sparks across the spark plug gap 3| for igniting a combustible charge in the cylinder of an engine.

Novel means are provided for controlling the discharge of condenser 2| across gap 23, 25 in properly timed relation to the speed of the engine on which the system is mounted. Said means comprises an auxiliary source of electrical energy which in the form illustrated, by way of example only, is constituted by a small magneto generator 33. This auxiliary magneto may, but need not necessarily be 'similar in construction to magneto |0. Asshcwn, magneto 33`comprises a four-pole magnetic rotor 34lassociated in a manner wellunderstood in the art with a two-pole stator 35,'- the poles of which are 'connected by a core on which a primary windin'g 3G- is wound. Said winding is connected in a conventional manner with a cam 'operated' circuit breaker 31 and a condenser 38;' as describ'ed above in connection with the primary circuitlof magneto' IC; For reasons to appear hereafter, cams I'l and 39 are operated in predetermined relation to one another so that circuit breakers |5 and 37 will be alternately opened and so that the points of circuit breaker iii will always be in closed or engaged position'at the instant that the points of circuit breaker 37 are moved to open position for interrupting the primary circuit of magneto 33. Auxiliary circuit breaker 3'l'is preferably closed during' the entire period that circuitl` breaker |5 is in open position, bothv of said circuit breakers beingfin closed positionduring an appreciable interval prior to each opening of circuit breaker 31;' This mode of operation of themain and auxiliary circuit breakers is not essential, but it is believed that best results may be obtained in this way.

The ungrounded or high 'potential end of winding 36 is connected to the primary winding 43 of a step-up transformer, the secondary winding 4| of which has the high potential end thereof connected to a third 01' auxiliary electrodc 42 in spark gap device' 24. The low potential ends of windings 40 and 4| may be connected to ground, as at 22.- The electrical and physical characteristics of magneto 33and transformer 45, Al are such that a relatively high voltage, a voltage of approximately five thousand volts having `ceen used' in one installation, is induced in'winding 4| whenever the points-of circuit breaker 3? are opened by cam 38. This induced'yoltage results from the Sudden surge of current in primary winding 40 which in turn results-primarily from self-induction at magneto winding 36"upon the opening of circuit breaker- 31. If desired, of course, the secondary winding 4| could be wound on stator 35 in inductive relation with winding 36 in accordance with conventional practice in high tension magnetos. This type'of auxiliary magneto is illustrated in Fig. 2.

The relatively high voltage induced in winding 4| is effective to create a discharge across the relatively wide gap between electrodes 25' and 42`and this discharge-is effective to ionize the relative wide gap between'electrodes` 23 and 25 to thereby permit a dischargeacross theV same at relatively low voltage. The main electrodes 23 and are placed so far apart that condenser 2| is incapable of discharging across the same until the intervening space isionized in the manner described above by the auxiliary source of energy. Danger of any bridging of the gap 23, 25 by building up of one 'of the 'electrodes and deterioration of the lother is thus substantially eliminated and the reliability of the circuit is accordingly greatly enhanced. This important result as well as accurate timing is -attained without employing a highrdistribution voltage.

The reactance of each of the spark plug circuits from electrode 25 through a primary Winding 29 is kept as low as possible to the triggering frequency, i. e., the `frequency in the circuit including secondary winding LH, so that said electrode is at substantially ground potential lwith respect to auxiliary electrode-42. Thus, the triggering or ionizing voltage which is generated by the low voltage--lovi7 energy source 33 is substantially dissipated -across the auxiliary gap 25, 42 and hence has little 01' no effect upon the high frequency coils 29, 3B. In order to minimize the radio shielding problem, the high voltage coil w, 4| and gap device 24 may be incorporated in a single shielded unit 43. The high voltage coil 29, and spark plug 3! may also be embodied in a unitary radio shield 44.

In the form illustrated in Figs. 3 and 4;, the novel spark gap device 24 comprises an hermetically sealed casing 45 of glass or other suitable material which encloses electrodes 23, 25 and 42 and is preferably filled with an inert gas, such as nitrogen, hydrogen, argon, or the like, under a pressure of approximately 1 or 2 atmospheres. Each of the electrodes 23, 25 and 42 is preferably constituted by a metallic plate, the major portion 45 of which is made of a metal having good heat conductviity, such as stainless steel, copper, or the like, and a tip portion 47 of tungsten or similar conductive material having high resistance to erosion by electrical arcs or Sparks. The tungsten tip of auxiliary electrode 42 is preferably placed nearer to electrode 25 than to electrode 23 but this is not essential. If desired, a condenser may be connected in series with auxiliary electrode 42.

In the operation of the embodiment of Fig. l, a unidirectional or unipolar charge is periodically built up in condenser 2! in the manner fully set out above. If desired, of course, the charge on condenser 2! may be built up by a direct current generator or the like without the use of a rectifier but this is not always suitable because the voltage developed by such a generator varies substantially with variations in the speed of the rotor. By reason of the wide spacing of electrodes 23 and 25 condenser 2i will not discharge until the intervening space is ionized by a triggering discharge between electrodes 25 and 42. This latter discharge oceurs whenever circuit breaker 31 is opened. The periodic high frequency discharges of condenser 2| across gap 23, 25 are effective as described above to successively energize the high frequency coils 29, 30 and cause a spark or shower of sparks across the spark plug gap 3| associated therewith. Rotors H and 34, cams ll and 39 and distributor arm 21 are all rotated by the engine in timed relation with each other so that the spark plugs in the various cylinders will be successively fired in properly timed relation to the operation of the pistons in the cylinders.

In the embodiment of Fig. 2 the method of distribution is changed in order to obviate the necessity of passing the main high frequency current through .a distributor. Instead of one three-electrodespark gap device 24 in series with condenser'i a plurality of such devices :are connected in parallel, one device being connected in circuit with each high frequency transformer 29, 32. The successiveselection of a proper spark plug circuit is accomplished `by means of aselector or distributor 48 which may be of the 'jumpgap type commonly used in high tension distribution ignition systems. The output terminale 49 of .selector 48 are connected to the auxiliary electrodes 42 of vthe various spark'gap devices 24 and the input terminal 'or rotary arm 52 is connected in circuit with 'the secondary or high potential winding of a high tension magneto generator 33. As shown, the latter is identical with the auxiliary magneto of Fig. 1 except that a secondary vwinding 5! is conventionally inductively coupled with the primary winding 36 and takes the place of transformer 45, 4| of Fig. l. It will be apparent, of course, that either vtype of auxiliary triggering or timing circuit for the gap devices 24 may be used in connection with either of the illustrated ignition circuits. If coils corresponding to coils 40, 4! were employed in the embodiment of Fig. 2 in lieu of the secondary winding 5|, one such coil could be placed ahead of selector 28 or one could be placed in circuit With each of the spark gap devices 24 between such device and a terminal 49 of selector 48.

Although only a limited number of embodiments of the invention are illustrated in the accompanying drawings and described in the foregoing specification, it is to be expressly understood that the same is not limited thereto. For example, the main and auxiliary or triggering sources of electrical energy need not necessarily be of like construction, as illustrated, and the circuit breakers as well as the Operating means therefor may be of any other suitable known construction. Other changes, particularly in the arrangement and disposition of the parts illustrated may also be made without departing from the spirit and scope of the invention as will now be clear to those skilled in the art. For a definition of the limits of the invention, reference is had primarily to the appended claims.

What is claimed is:

l. In an ignition circuit or the like of the condenser discharge type, the combination of a storage condenser, and means for controlling the discharge of said condenser, said means including a spark gap in a gaseous medium in series with the condenser and means for yperiodically ionizing the gaseous medium in the vicinity of said gap including the secondary winding of a transformer in circuit with an auxiliary electrode adjacent one of the main electrodes of said spark gap, means for periodically energizing said transformer including a circuit breaker connected in parallel with the primary winding of said transformer and across an induction coil, magnetic means including a rotor for energizing said induction coil and cam means operable in timed relation with said rotor for periodically opening said circuit breaker, whereby said transformer is periodically energized by the self-inductive kick of said induction coil.

2, In an ignition circuit or the like of the condenser discharge type, the combination of a storage condenser, means for charging said condenser, and means for controlling the discharge of said condenser, said controlling means ineluding a spark gap in a gaseous medium in series with the condenser and means for periodically ionizing the gaseous medium in the vicinity of said gap, said last named means including a magneto generator having a primary circuit including a periodically operated circuit breaker and a secondary cireuit inductively coupled with said primary circuit and including an auxiliary electrode adjacent one of the main electrodes of said spark gap.

3. An igniton circuit or the like as defined in claim 2 comprising a plurality of said spark gaps connected to the storage condenser and in -pa1'al1e1 with each other, an auxiliary electrode adjacent one of the main electrodes of each of said spark gaps, and a distributor in the secondary circuit of the magneto generator and operable in timed relation to said circuit breaker for successvely connecting said auxili-ary electrodes in said secondary circut, whereby said spark gaps are rendered conductve to the charge on said storage condensei` in predetermined succession.

JOHN V. MCNULTY.

8 REFERENCES orrEn The following references are of record in the file of this patent:

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